The Transportation Security Administration has called for increased security measures for passengers flying to the U.S. from certain countries amid fears that terrorists have developed new bomb-making techniques.

During screening of passengers flying to the U.S., airport screeners may ask travelers to power on their electronic devices, such as cellphones. Devices that won't power up won't be allowed on the plane, TSA officials said.

Cellphones on planes

Robert Nickelsberg / Getty Images

The Transportation Security Administration is heightening security measures for flights to the U.S. from certain countries. Above, passengers prepare to get off a JetBlue Airways flight after landing in Long Beach.

The Transportation Security Administration is heightening security measures for flights to the U.S. from certain countries. Above, passengers prepare to get off a JetBlue Airways flight after landing in Long Beach. (Robert Nickelsberg / Getty Images)

"As always, we will continue to adjust security measures to promote aviation security without unnecessary disruptions to the traveling public," said Department of Homeland Security Secretary Jeh Johnson.

In most foreign countries, TSA screeners do not screen passengers but can dictate security procedures for direct flights to the U.S.

TSA officials declined to provide more details about the enhanced screening process but counter-terrorism experts have recently told the Los Angeles Times that a bomb maker working for Al Qaeda in the Arabian Peninsula had created a technique for hiding explosives that could evade existing metal detectors, body scanners and pat-downs.

Officials are concerned that the method could be shared with rebel fighters in Syria who are from Western nations and might have valid passports and visas that would allow them to board a flight to the U.S.

Although TSA officials did not say which airports will experience the heightened security measures, counter-terrorism officials say travelers can expect increased screening while flying to the U.S. from the Middle East and Europe.

To read more about travel, tourism and the airline industry, follow me on Twitter at @hugomartin.

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